[Refactor] improve performance of component detection

[golopot]

Some node visitors for components detection are redundant.

Benchmark with time npx eslint . (mean of 5 runs):

- 5.06 s
+ 5.01 s

[codecov]

Codecov Report

Merging #3276 (ea3b2a3) into master (ea3b2a3) will not change coverage.
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@@           Coverage Diff           @@
##           master    #3276   +/-   ##
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  Coverage   97.72%   97.72%           
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  Files         123      123           
  Lines        8744     8744           
  Branches     3165     3165           
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  Hits         8545     8545           
  Misses        199      199           

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[ljharb]

Can you elaborate on how they're redundant?

[golopot]

Our heuristics for detecting function components is checking if the function returns jsx or null (isReturningJSX), this function is expensive to execute. In a simple test case isReturningJSX is found to run 3 times for a simple function, ideally it should run only once.

This part is redundant

eslint-plugin-react/lib/util/Components.js

Lines 829 to 840 in 24621e4

	ReturnStatement(node) {
	if (!utils.isReturningJSX(node)) {
	return;
	}
	node = utils.getParentComponent();
	if (!node) {
	const scope = context.getScope();
	components.add(scope.block, 1);
	return;
	}
	components.add(node, 2);
	},

, because checking isReturningJSX is included in getParentComponent -> getParentStatelessComponent -> getStatelessComponent -> isReturningJSX.

eslint-plugin-react/lib/util/Components.js

Lines 785 to 796 in 24621e4

	FunctionDeclaration(node) {
	if (node.async) {
	components.add(node, 0);
	return;
	}
	node = utils.getParentComponent();
	if (!node) {
	return;
	}
	components.add(node, 1);
	},

[ljharb]

Would it be simpler to memoize isReturningJSX?

[golopot]

Would it be simpler to memoize isReturningJSX?

No, it wouldn't. Deleting redundant code is better than adding memoizing.